使用实体框架插入/保存具有嵌套子实体的实体

Question

以下是课程：

public class Parent 
{
     public int Id { get; set; }
     public string Name { get; set; }
     public IEnumerable<Child> Childs { get; set; }
     public IEnumerable<ParentLog> Logs { get; set; }
}

public class ParentLog 
{
     public int Id { get; set; }
     public DateTime On { get; set; }
     public string Note { get; set; }
     public int ParentId { get; set; }
     public string Name { get; set; }
}

public class Child 
{
     public int Id { get; set; }
     public string Name { get; set; }
     public int ParentId { get; set; }
     public IEnumerable<ChildLog> Logs { get; set; }
}

public class ChildLog 
{
     public int Id { get; set; }
     public DateTime On { get; set; }
     public string Note { get; set; }
     public int ChildId { get; set; }
     public string Name { get; set; }
     public int ParentId { get; set; }
}

在DbContext:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
     modelBuilder.Entity<Parent>().HasMany(a => a.Childs);
     modelBuilder.Entity<Parent>().HasMany(a => a.Logs);
     modelBuilder.Entity<Child>().HasMany(a => a.Logs);
}

这个想法是当父母和孩子被保存时，父母和孩子的日志条目也被保存。这行得通。

保存代码：

DateTime now = DateTime.Now;
foreach (var a in parents)
{
     a.Logs = new List<ParentLog>();
     a.Logs.Add(new ParentLog
     {
          On = now,
          Note = "Created",
          Name = a.Name
     });

     foreach(var b in a.Childs)
     {
         b.Logs = new List<ChildLog>();
         b.Logs.Add(new ChildLog
         {
              On = now,
              Note = "Created",
              Name = b.Name,
              ParentId = b.ParentId //not needed with the Accepted Answer.
          });
     }
}

int recordsAffected = new ParentRepository().SaveParents(parents);

public int SaveParents(List<Parent> items)
{
     foreach(var item in items)
     {
          _db.Parents.Add(item);
     }

     return _db.SaveChanges();
}

我遇到的问题是ChildLog.ParentId。它没有预期值的值，我想是来自Child.ParentId。

我的问题，如何解决？

Answer 1

向 Child 模型添加导航属性 ChildLog >Child。

然后您就可以通过 Child 访问 ParentId。

进一步阅读 - https://docs.microsoft.com/en-us/ef/ef6/fundamentals/relationships

Answer 2

事实证明 EF 可以在一个 SaveChanges() 中处理它。不过，我需要明确定义关系。

以下是已更新的类：

public class Child 
{
     public int Id { get; set; }
     public string Name { get; set; }
     public int ParentId { get; set; }
     public IEnumerable<ChildLog> Logs { get; set; }
     //Added
     public Parent Parent { get; set; }
}

public class ChildLog 
{
     public int Id { get; set; }
     public DateTime On { get; set; }
     public string Note { get; set; }
     public int ChildId { get; set; }
     public string Name { get; set; }
     public int ParentId { get; set; }
     //Added
     public Child Child { get; set; }
}

这是 DbContext 中更新后的 OnModelCreating 方法：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
     var parent = modelBuilder.Entity<Parent>();
     parent.HasKey(a => a.Id);
     parent.Property(a => a.ParentId).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
     parent.HasMany(a => a.Logs); //ParentLog

     var child = modelBuilder.Entity<Child>();
     child.HasKey(a => new { a.Id, a.ParentId });
     child.Property(a => a.ChildId).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
     child.HasRequired(a => a.Parent).WithMany(a => a.Childs).HasForeignKey(a => a.ParentId);

     var childLog = modelBuilder.Entity<ChildLog>();
     childLog.HasKey(a => new { a.Id, a.ChildId, a.ParentId });
     childLog.Property(a => a.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
     childLog.HasRequired(a => a.Child).WithMany(a => a.Logs).HasForeignKey(a => new { a.ChildId, a.ParentId });
}

这对我有帮助 -> How to fix: The number of properties in the Dependent and Principal Roles in a relationship constraint must be identical?

这件小而重要的事情真是麻烦。